Pulse-forming preamplifier



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8 Sheets-Sheet 8 JNVENroA QUENT//v A. /fE/efvs A Tram/Ey Patented ug. 8, 195@ PULSE-FORPJHNG PREAMPLIFER Quentin A. Kerns, Berkeley, Calif., assigner to the United States oi' An the United States Ato nerica as represented by zinc Energy Commission Application Alpril 5, 1948, Serial No. 18,927

s claims. (ci. a-'27) This invention relates to an electronic control circuit and more particularly to method and apparatus for the control of frequency modulated systems.

In the operation of a frequency modulated circuit, it is often desirable to control the output of the circuit in response to a selected frequency. The present invention accomplishes this control by utilizing a combination of several circuits to transform a frequency modulated signal voltage into a rectangular voltage pulse of variable duration occurring at a predetermined rate in response to a selected frequency within the frequency range of the frequency modulated signal Voltage.

It is therefore an object of the invention to provide a new and improved method and apparatus for the electronic control of a frequency modulated circuit.

Another object of the invention is to provide a circuit which will generate a voltage of variable duration at a predetermind rate.

Still another object of the invention is to provide a circuit which will generate a voltage of variable duration at a predetermined rate in response to a selected frequency within the range of frequency of a frequency modulated signal.

A still further object of the invention is to provide an electronic control circuit having a pulse selector circuit whereby the frequency of the output voltage can be varied as desired.

Other objects and advantages of the invention will be apparent in the following description and claims considered together with the accompanying drawings in which:

Figure 1 is a block diagram showing the power distribution from the power supply to the various circuits of the invention;

Fig. 2 is a block diagram showing the manner in which signal voltages are interconnected between the various circuits of the invention;

Fig. 3 shows the wave form of voltages at indicated positions in the Various circuits of the invention;

Fig. 4 is a schematic wiring diagram of the limiter and discriminator circuits;

Fig. 5 is a schematic wiring diagram of the pulse generator and frequency selector circuits;

Fig. 6 is a schematic wiring diagram of the diierentiator and amplifier circuit;

Fig. 7 is a schematic wiring diagram of the pulse type selector and gate circuits; and

Fig. 8 is a schematic wiring diagram of the trigger and one-shot multivibrator circuits.

Referring to the drawings in detail, there is 2 shown in Fig. 1 a power supply I0 which has an external connection I I to a standard alternating current source. The power supply I EJ furnishes unidirectional operating voltages I2, I3, III, IE, I l and aconnnon ground connection I8. The voltages I2, I3, I4, and I5 are positive and the values of thesevoltages decrease from the highest voltage I2 to the lowest voltage I6. The 'voltage Il is negative in value. Also shown in Fig. 1 are blocks representing the circuits of the invention; namely, a limiter circuit 20, a discriminator circuit Sil, a pulse generator circuit 40, a frequency selector circuit 50, a diierentiator and amplifier circuit '68, a pulse type selector circuit 18, a gate circuitBIl, a trigger circuit` 9B, and a one-shot multivibrator circuit It. The

distribution of the voltages supplied bythe power supply Ill to the various circuits of the invention is shown schematically. `A detailed discussion of the connections to the voltages will be given in the description of the circuits hereinbelow.

Fig. 2 shows the circuits in block form as in Fig. l and shows the signal voltage connections between the circuits. An input lead `III is connected from an external frequency lmodulated system to the limiter circuit 20 andto the frequency selector circuit 523." Anoutput lead H2 `of the limiter `circuit `2Il` is connected to the discriminator circuit 3lI.` An output lead H3 of the discriminator circuit (it is connected to` the dilerentiator and amplifier circuit Eil. A connecting lead I It is connected from the output oi the differentiator and ampliiier circuit E@ to the pulse generator `circuit it andto the gate circuit ll. The output of the pulse generator circuit 4Il is connected to thepulsev type selector circuit it] by a lead IIB.` A lead II'I connects the pulse type selector circuit l0 to the gate circuit Si). The gate circuit is connected to the frequency selector 5c by a lead IIB and is connected to the trigger circuit all by a lead H9. A connection is made from the trigger circuit 9i) to the pulse type selector 'lll by a lead I2I and to the one-shot multivibrator circuit |00 by a lead |22. A lead I23 serves as the output terminal for the invention and is connected to the output of the one-shot multivibrator circuit IDI). I

Fig. 3 shows several time correlated voltage wave forms of voltages at various referenced positions throughout" the circuits of the invention. Discussion of these voltages and their wave forms will be made in the descriptions of the circuits.

In Fig. 4 the input `lead III is shown connected to the |control grid f a pentode type limiting tube through a limiting resistor |52 and to the ground connection I8 through a grid biasing resistor |53. The cathode of this tube i5| is directly connected to the suppressor grid by a lead |511 and to the ground connection i6 thirough a parallel circuit comprising a by-nass condenser |56 and a cathode resistor |5. The screen grid of the tube |5| is directly connected to the positive voltage I6 by a lead |58 and to the ground connection I8 through a by-pass condenser |59. The anode of this tube |5| is connected to the positive voltage i6 through an anode resistor |6|. The output lead H2 is connected to the anode of the tube |5| and serves as a point from which the output voltage of the limiter circuit 26 is taken.

Considering the operation of the limiter circuit 26, e, frequency modulated signal as shown on Fig. 3--A is impressed at the cathode of the tube |5l. The control grid voltage of the tube 25| follows the signal voltage until the control grid becomes positive with respect to the cathode of the tube, at which time grid current flows. The grid current produces a voltage drop across the limiting resistor |52 which opposes the signal voltage, thereby producing the limiting action, in that the positive peaks of the signal voltage above a p-redetermined value have no effect on the operation of the tube |5|. Thus the anode voltage of the tube |5| is that shown on Fig. 3--B for the lea'd ||2. The predetermined value of voltage at which the limiting action occurs can be set by the values of the resistors |52 and il and the condenser |56.

Also shown on Fig. 4 is the discriminator circuit 30 which derives its signal voltage from the lead ||2. The lead ||2 is connected to one side of a tuned circuit comprising a variable condenser |62 and the primary winding of 1a. transformer |63. The other side of this tuned circuit is connected to the positive voltage i6. The transformer |63 has two secondary windings |64 and |66. One terminal of the secondary winding |64 is connected to one side of a variable condenser |6'|', a resistor |68 and a crystal rectifier |69, the latter of which is, in turn, connected to one side of a condenser and a resistor H2, and to the ground connection I3. The other terminal of the secondary winding |64 is connected to the remaining side of the condenser |671, the resistor |68, the condenser Ill, and the resistor |12. One terminal of the secondary winding |56 is connected to one side of a variable condenser |73, a resistor |14, land a crystal rectifier H6, the latter of which is, in turn, connected to one side of a condenser |71, a resistor |76, and to the un grounded side of the resistor H2 through `a resistor |76. The other terminal of the secondary winding |66 is connected to the remaining side of the condenser |73, the resistor lili, the condenser lll, the resistor |78, and is further connected to the control grid of a triode type cathode follower tube |3| through a resistor |62. The anode of the tube |6I is directly connected to the positive voltage I3 by a lead |66. The cathode of the tube |8| is connected to the negae tive voltage l1 through a cathode resistor iti-i', A lead i3 is also connected to the cathode of the tube |6l and serves as a source of output voltage for the discriminator circuit 36.

In operation, the lead l2 supplies a voltage shown on Fig. 3-B tothe primary winding the transformer |63. The primary winding or the transformer |53 and the condenser |62 form a tuned circuit |66 which is tuned to a resonant frequency, which is the mean frequency of the frequency modulated signal voltage, by the adjustment of the variable condenser |62. The secondary winding |66 and the condenser |611 form a second tuned circuit mi which is tuned to a resonant frequency slightly above the mean frequency of the signal voltage by the adjustment of the variable condenser |6l. The sec' ondary winding 566 and the condenser H3 form a third tuned circuit G66 which is tuned to a resonant frequency slightly below the mean frequency of the signal voltage by the adjustment of the variable condenser il. The resistors |65, |68, and VM lower the Q of the transformer windings sufficiently that a band-pass frequency response is obtained. Now, assume that the frequency modulated signal voltage has reached its maximum frequency. Under this condition the resonant frequency of the tuned circuit ll differs from the frequency of the signal voltage by a minimum amount and a maximum value of current flows in the tuned circuit ist. At the same time, the resonant frequency of the tuned circuit 66 differs from the frequency of the signal voltage by `a maximum amount and a minimum. value of current iiows in the tuned circuit E68. With a maximum value of current flowing in the tuned circuit H61, a maximum value of voltage is developed across the resistor 263. The voltage across the resistor |68 is then rectied by the crystal rectifier |66 and developed across the resistor il?. The connections of the discriminator circuit are such that the polarity of the voltage developed across the resistor I'l2 is negative at the ungrounded side. Now, as the `frequency of the signal voltage decreases from its maximum value, the current iiowing in the tuned circuit |66 decreases and the current flow ing in the tuned circuit |86 increases. This action continues until frequency of the signal vo tage reaches its minimum value, at which time a minimum value of current flows in the tuned cir-- cuit i6? and a maximum value of current ows in the tuned circuit |66, Under the latter condition a maximum value of voltage is developed across the resistor |l8 having a polarity such that the side away from the ground connection |6 is positive. :from the foregoing it is seen that a voltage is developed across the resistors |72, |"l9, and |76 which is negative by a maximum value at the highest frequency of the signal voltu age, zero at the mean frequency of the signal voltage, and positive at the lowest frequency of the signal voltage. This .alternating voltage is impressedon the control grid of the tube |S| which is connected as a cathode follower and serves to isolate the discriminator from the circuits 'which follow. The lead i i3, which is connected to the cathode of the tube 58|, furnishes an output voltage as shown on Fig. B-C.

Referring now to Fig. 5, the lead hi furnishes a voltage, as shown on Fig. 3--G, the development of which will be discussed hereinbelow with the description of the differentiator and amplifier circuit 66, to the pulse generator circuit dil. The voltage of the lead iid is coupled to the control grid of a gas discharge type triode tube E62 through a series connected condenser and resistor 62, The control grid of the tube 286 is connected to the ground connection i6 through a grid biasingresistor |93. A cathode resistor i534 is connected between the cathode of the tube |69 and the ground connection i6. A oy-pass condenser |66 is connected in parallel with the resistor |94. `The cathode of thetube |88 is connected to the anode through `a series connected resistor |91 and condenser |98 and tothe positive voltage I3 through a resistor I 89. A dropping resistor 20| is connectedl between the positive voltage I3 and the anode of the tube |88. The output lead I I8 of the pulse generator circuit 40 is connected to the anode of the tube |39. i

In operation the pulse generator circuit 40 generates sawtooth voltages at arate predetermined by the values of the anode resistor 20| and the condenser |98. This rate is usually set at a submultiple of the frequency of the frequency excursions of the frequency modulated signal voltage. The tube |89 and its associated elements constitutea free running relaxation oscillator; that is, the condenser |38 charges slowly through the `resistor 20| until the ring voltage .of the tube |89 is reached, at which time the tube con- I ducts and the condenser |98 discharges. `The cycle then repeats with the charging of the condenser |98. The square wave of voltage `of the lead II4 as shown on Fig. 3--G is connected to the control grid of the tube |89 through a dif ferentiator comprising the condenser ISI and the resistors |92 and |93. This results in a posi tive pulse of voltage being impressed on the con trol grid of the tube |89 at the time the square wave of voltage becomes positive and a negative pulse at the time the square Wave of voltage be comes negative. These pulses of voltage have no effect on the operation of the tube |89` until a positive pulse occurs at a time when the con.. denser I98 has almost attained maximum charge. Under this condition the firing voltage of the tube |89 is lowered and the tube conducts, causing the frequency of the pulse generator to fall into synchronism with a submultiple ofthe frequency of the frequency excursions of the modulated signal voltage. Thus the output lead IIB of the pulse generator circuit 40 serves as a source of positive sawtooth voltages which are synchronized as explained above.

Also shown on Fig. 5 is the frequency selector circuit 58 which is supplied the voltage of Fig. B A by the lead III. This lead III is connected to the ground connection I 8 through a resistor 202 and to the third grid of `a multigrid converter tube 203 through a grid current limiting resistor 204. The first grid of the tube '203 is connected to the ground connection I8 through a grid biasing resistor 288 and to a tuned circuit 201 through a coupling condenser 208. The tuned circuit 201 comprises the parallel connected condensers 200 and 2II, and a coil 2I2. One side of the tuned circuit 20'! is connected to the condenser 208 and the remaining side is connected to the ground connection I8. The cathode of the tube 203 is connected to the fth grid of the tube by alead 2I3 and to a tap on the coil 2|2 by a lead 2I4. rihe second and fourth grids of the tube 203 are connected by a lead 2I8 which is connected to the ground connection I8 through a condenser 2I'I and to the positive voltage I3 through a resistor ZIB. The anode of the tube 203 is connected to one end of both of the two windings 2 I 9 and 22E `of a band-pass transformer 222 and to one side of a variable condenser 223 which is connected in paralle1 with the winding 22|. The other end of the winding 2|9 is connected to the positive voltage I3 by a lead 224. The other end of the winding 22| is connected to the junction of two resistors 226 and 221 which are connected between the positive voltage I3 and the ground connection I8. The junction between the anode of 'thextubei 203 and the condenser 223 is con-'- nected `toa crystal rectier 228 which, in turn, is connected to the ground connection through a resistor '229 and to the lead ||8 through a coupling condenser23I.

In operation the lead III furnishes a voltage as shownon FigfS-A to the third grid of the Aconverter tube `203 of the frequency `selector circuit- `50. The tube '203 is so connected that the elements. connectediinto the circuit of the first grid form `aflocaloscillator which oscillates at a frequencydetermined by the Value of capacitance of thecondensers 209 and 2II and the value of the inductance of the coil2I2. The condenser 208 servesl as ameansfor coarse adjustment and the condenser 2| I for ne adjustment of the frequency ofthe oscillatory circuit. Theband-pass transformer in Ithe anode circuit of the tube is `adjustable by meansof the condenser 223. Now,

with .the condensers 20,9 and `2| I so adjusted that the oscillator frequency is higher than the maximumfrequency of the signal voltage of the lead IIIya voltage is impressed on the winding 2I9 which has a frequency equal to the sum of the two frequencies anda frequency equal to the difference` of the two frequencies. From the foregoing it` is seen that by adjusting the variable condenser223 it is lpossible to obtain. an output voltage from the band-pass transformer 222 at any desired frequency. Thus, if it is desired to obtain an output pulse of voltage at 10 megacycles when the frequency excursion of the signal voltage ranges from 9 to 13 megacycles, the con- Vdensers 209 and 2| I should be adjusted for a local oscillator frequency of 14 megacycles, and the condenser 223 adjusted for passing voltages having a frequency of 4 megacycles. Under these conditions a short pulse of voltage will be impressed at the crystal rectifier 228 twice during each frequency excursion of the frequency modulated signal voltage, `once as the frequency is increasing and once as the frequency is decreasing. The crystal rectifier 228 is so connected .that the positive portion of the pulses are removed, thereby `developing negative pulses of voltage across the resistor 229, which are coupled :to the leadI I 8 by the condenser 23 I. The voltag .of the lead IIBis as shown onFig. 3--H. Consider now Fig. 6 which shows the lead II 3 connected to the control grid of a triode type tube 232 through a coupling network comprising a resistor 233 and a condenser 234.V The cathode `of the tube 232 is connected to the negative voltage I'Ithrough a biasing resistor 236 and a by- Apass condenser 231. A resistor 238 connects the anode tothe control gridof the tube 232. The anode of the tube `23.2 is further connected to the positive voltage I3` through a dropping resistor 239 and to the control grid ofa triode tube 24| through a4 coupling `condenser 242. The control grid of the tube 24| is connected to the junction of the two resistors 243 and 244, Whichare connected between the negative voltage I1 and the ground connection I8, through a resistor 246. Other connections of the tube 24| are as follows: .the anode lis directly connected to the positive voltage I3 by a lead 241, and the cathode is connected to the negative voltage I1 through a biasing resistor 248 and to the control grid of a triode tube 249 by lead 25|. Thecathode of the tube 249 is directly connected to the ground connection I8 by alead 252. The anode of the tube 249 is connected to the positive voltage I3 through a dropping resistor 253 and to thecontrol grid of a triodetube 254 through acoupling condenser 25B.

27 The control .gridof i'.he tube 42.54 is connected to the junction Lof two resistors .251 `.and 25.8, which are connected between the negative voltage I1 and the ground connection :I 8, Yfthrough .a .resistor ground connection :L8 through .a by-.pass condenser 2.98 and to the junction of :two :resistors 269 and 21| of a -izoltage .divider :between :the .positive voltage :I3 4and `.the ground connection lI'8, and the anode is :connected to the positive voltage I3 through a dropping resistor 212 .and to the lead I I4.

In operation, lthe lead II'3 .supplies :the differentiatorand :amplifier .circuit :69 with a voltage as shown on Fesc. lThe amplier :time

and its associated .elements .are .connected in such a manner `that the voltage @of the lead fl I'3 is yinverted and amplified at 'the :anode of the tube. "The voltage at the anode .of `the tube :232 is .shown on Fig. S-D and is impressed on the differenti- `ator circuit comprising the condenser 24.2 :and the resistors 2146, 243, and 244., 'the values of which are such that the phase .of the voltage is shifted by 90 degrees .as shown von Fig. 3-E. Thus the point of zero amplitude of the .alternating voltage corresponds to the point A.of maximum frei quency of the frequency lmodulated signal voltage. The output voltage of the :differential-,or circuit is impressed on the control grid .of the cathode follower tube '24d which drives zthe plate loaded amplier tube .2.4.9. `The ytube 249 `:is supplied operating voltages by the connections describedabove, such that the control Agrid .becomes suiciently positive during the lpositive portion of the alternating voltage "to overdrive vthe tube. rThe effect .of this is -to produce a voltage at the anode of the tube `2.49 such as is shown on Fig. 3--F, which is impressed ,on the control grid .of the cathode follower tube'254.. Since the .tube 254 is a cathode follower, :the control grid of the amplifier' tube 263 :is driven Aby ar voltage substantially the .same as that of Fig. 13-F. This tube is supplied :operating voltages which cause .the tube to .fbe `,overdriven vduring the most posi- .tive A:portion of :the voltage impressed at its control .grid and a clipping action takes place during this lportion of the voltage cycle. Therefore the Avoltage at the .anode of `the tube 263 is substantially a square wave as shown on 11B-G. Since the output lead :I I4 is connected to the anode of the tube :26.3, its voltage .falso that of Eig. .B-G.

in Fig. 'I is yshown fthe lead I`2I which is connected to the v.control grid of a triode tube 213 through `a coupling .condenser 214 in the pulse Atube'selector circuit 1D. vThe control Ygrid of the tube :213 is connected 'to the `negative vol-tage I1 through a biasing resistor 21.6. Other connections .Of .the vtube 2113 are as follows: the cathode directly connected vto the ground connection I8 `bye Alead 2121,1and the `anode is connected to the positive yvoltage lil through .a dropping resistor 211B and further to the control grid .of a triode 'tube `21:9 through .a coupling network 28I comprising a parallel connected resistor 282 and condenser l283. The control grid of the tube 8 219 is connected to .the negative voltage I1 through a biasing resistor 284. Further connections to the tube 219 are as follows.: the cathode is directly connected to the ground connection I8 by a lead 286, and the anode is connected to the positive voltage I3 through a dropping resistor 281 and to the control grid of the tube 213 through a coupling network 288 comprising a parallel connected resistor ,289 and condenser 29|. Also shown as part of the pulse selector circuit 10 are 1two ganged selector switches 292 land 293. Each switch has ve positions with a contacting arm operating from a central position. Position No. .3 .of the selector switch 292 is the .only position to which a connection is made Aand this connection is the lead II6. The contacting arm ofthe switch 292 is connected to the control grid of vthe tube 219 through Ya coupling condenser 294. Position No. l of the switch 293 is directly connected to the ground connection I8 -by a lead 2196, `position Nlo. 2 is connected to the negative voltage l1 through a resistor 291 and to the grou-nd Aconnection I8 through a bypass condenser 298, and position No. 3 is ldirectly connected to the control grid of the tube 219 by a lead 299. The contacting arm of the switch 293 is connected to `the lead I-I1 which serves as a source of output voltage for the pulse selector circuit 19.

The tubes 213.and 219 and their associated elements of the pulse type selector circuit 1I! are in- :terconnected in the form of .an electronic switch or better known as a flip-flop circuit. The tube A219 is normally conducting and the tube 213 is normally nonconducting. The action of the flipflop circuit is conventional in that a negative voltage impressed at the control grid of the tube 219 causes this tube to become nonconducting and the tube 213 to become conducting. To return the circuit to its vnormal operating condition, it is then necessary to impress a negative voltage at the control grid of the tube 213. Control of the output voltage of the entire circuit of the invention is obtained by the lvarious settings of the selector switches 292 and 293. With the switches .292 yand 29S set .at position No. 1 the circuit is off and ythere is no output voltage, as will be explained more fully hereinafter. With the switches292 and .293 in position No. 2, the voltage of the lead II1 becomes negative through the resistor 291 and condenser 293 combination, and the .eiects .of this will be explained more fully hereinbelow. New, with the switches 292 and 293 in position No. 3, the flip-nop circuit of the pulse type selector circuit 1i] becomes effective, in that the lead II is connected to the control grid of the tube 219 through the switch 292 and .the condenser 294, and the control grid of the tube 219 is connected to the lead l l1 through the switch 293. Under this condition, the tube 219 is conducting, thereby placing a positive voltage on the control grid of the tube 219 and on the lead II1. Since `the condenser l294 and the resistor 284 form a differentiator circuit, a negative .pulse of voltage vis .impressed on the control grid of the tube 21.9 at the end of each sawtooth voltage of the lead H6, thereby causing the tube 21:9 to become nonccnducting and the tube 213 -to become conducting. Thus the lead I l1 carries a negative voltage during the time the tube 213 is conducting. `This condition remains until a .negative voltage is impressed on the control grid of the tube 233 by the lead I2l, which then returns the flip-flop circuit to normal and the voltage ofthe lead I'I1 toa positive value.

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Also shown on Fig. 7 is the gate circuit 3|), which shows the lead IIli connected to the control grid of a triode tube `30| through a grid limiting resistor 332. The controligrid of the tube 30| is connected to the negative voltage I1 through a biasing resistor 333. The cathode of the tube 33| is directly connected to the ground connection i8 by a lead 321|. A dropping resistor 3D3 is connected between the positive voltage i3 and the anode of the tube 30|. `A further connection of the anode of the tube 30|y is made to the anode of a triode tube 33|. The lead EIB is connected to the control grid of the tube 331 which is connected to the ground connection is through a biasing resistor 303. The cathode of the tube 337 is directly connected to the ground connection |8 by a lead 309. The anode of the tube 331 is further connected to the anode of a triode tube 3| I and to the lead ||9. The cathode of the tube 3|| is directly connected to the ground connection 8 by a lead 3 2. The lead Il is connected to the control grid of the tube 3| I'.

The operation of the gate circuit 33 is controlled by the selector switches 292 and 293 ofthe pulse type selector circuit i3. With the switches 292 and 233 in position No. 1, the control grid of the tube 3H is held at ground potential by the lead I|i. Since the anode of tube 3II is positive, the tube conducts thereby holding the output voltage at the lead H9 at. a minimum value. With the switches 292 and 233 inposition No. 2, thenegative voltage of the lead ||1 holds the tube 3H in a nonconducting state and any voltages gen" erated in the anode circuit of the tubes 33| and 331 appear at the lead H3. While the tube 3I| is nonconducting, the voltages impressed at the control grids of the tubes 33| and 331, by the leads I Iii and 3 respectively, control the output voltage. During the positive portion of the voltage of the lead lll, which is shown on Fig. S-G, the tubes 33| and 301 are both conducting heavily, thereby causing the anode voltage of the tubes to be at a minimum value. Under this condition, any negative voltage impressed at the control grid of the tube 301 by the lead H8 causes the tube to cease conducting for the duration of the negative voltage; however, since the tube 30| is conducting heavily, the change in the anode voltage of the tubes is very slight. Therefore the negative pulse in the voltage of the lead IEB, which is shown on Fig. 3-1-1, occurring during the time the frequency of the voltage of the frequency modulated signal voltage is increasing, is successfully `swamped out. When the negative portion ofthe voltage of the lead |13 is impressed on the control grid of the tube 33|, this tube becomes nonconducting. Now, When a negative voltage is impressed at the control grid of the tube 337 by the lead H3, the tube 331 becomes nonccnducting and the anode voltage then increases very rapidly and remains positive for the duration of the negative voltage at the control grid. Since a negative pulse of voltage is impressed at the control grid of the tube 331 by the lead I i 3, the anode voltage and therefore the voltage of the lead iig is a sharp positive pulse of voltage, as shown on Fig. 3`-J,`"occu.rring once during the descending frequency of the frequency modulated signal voltage. With the switches 232 and 233 in position No. 3, the tube 3| I is conducting because the control grid of the tube is positive, and thereby maintaining the gate circuit 83 cioted. Wlen a sav/tooth voltage is generated by the pulse generator circuit lil), the flip-flop circuit of the pulse type selector circuit 13 operates to place a negative voltage at the control grid of the tube 3| i, which opens the gate circuit. This condition remains until a negative pulse of voltage causes the tube 301 to become nonconducting While the tube 33| is maintained negative by the negative portion of the voltage of the lead H4. At this time a positive pulse of voltage is developed at the anodes ofthe tubes 30| 301, and 3| I which appears at the lead H9. Shortly after the developrnent of this positive pulse of voltage at the lead ||3, the voltage of the lead I 2| causes the iip-iiop circuit of the pulse type selector circuit lil to operate and close the gate circuit 8U. This procedure is then repeated at the rate of the frequency of the output voltage of the pulse generator 3U.

Referring tc 3, the lead HS is connected to the control grid of a gas discharge tube 3|3 through a grid limiting resistor 3Il| in the trigger circuit 33. The control grid of the tube 353 is connected tc the negative voltage ii through a biasing resistor 3|6. Other `connections of the tube 353 are as follows: the cathode is directly connected to the ground connection i3 a lead f 3H?, and the anode is connected to the positive voltage i2 through a resistor 3H! and to the positive voltage i6 through a pair of crystal rec tiiiers 3|@ and 32 i. The anode of the tube 3|3 is further connected to the lead I2| through a resistor and to the lead |22 through a con denser 323.

The lead H3` furnishes positive pulses or voltage to the trigger circuit 9B as described above. The operating voltages supplied to the tube 3|3 are such. that the tube conducts only during the time oi the positive pulses of voltage which are impressed by the lead I I3 on the controi grid of the tube. nested that the condenser 323 is charged to a conn i stant value during the time the tube 3|3 is nonconducting and thereby forms a uniform pulse ci voltage when the tube 3|3 conducts and discharges the condenser. The negative pulse `of voltage is developed at the anode of the tube 3|?) and appears at the leads |2| and |22. The voltage of the leads 2| and `i 22 is shown on Fig. 3-K.

Also shown on Fig. 8 is the `one-shot multivibrator circuit iilil, wherein the lead |22 is connected to the cathode of a pentode tube 323. The cathode of the tube 326 is .further connected to the suppressor grid by a lead 321 and to the ground connection i8 through a resistor 323. Other connections of the tube 323 are as follows: the control grid is connected to the negative volt y age il through a biasing resistor 323, the screen resistor 33'? and to the positive voltage |13 through series connected resistor 333 and potentiometer` 333. The cathode of `the tube 335 is connected to the ground connection I3 by a lead 34| and to the suppressor grid by a lead 342. Further connections ci the tube 333 are as follows: the screen i grid isconnected to the screen grid of the tube 323 by a lead .M3 and the anode is connected to the positive voltage i3 through a dropping resistor The anode of the tube 336 `is, further cone nected to the positive voltage I6 through a crystal 333 and to the control `grid of a pentode tube- The crystals 3i@ and 32| are so con- Stil' through a coupling condenser Stil. 'lhe control grid of the tube .'ifi'l' is also connected to the junction of two resistors 349- and 35i, which are serially connected between the positive y .-.tage i3 and the ground connection I8 through a resistor i352. Further connections of the tube li'l are as follows: the anode is connected to the positive voltage by a lead the suppressor grid is connected to the cathode by a lead 355i, the screen grid isconnected to the anode through a dropping resistor and to the cathode through a condenser and the cathode is connected to the control gridicf the tube through a parallel connested resistor and condenser and fur ther tothe ground connection lil through two series connected resistors 315i and Stil. The'junction of the two resistors 556i and is connected to the lead 23.

In operation the oudshct multivibrator circuit l'llfi' transforms a negative pulse of voltage impressed by the lead H22 into a positive rectangular pulse of voltage of variable duration at the lead I23, as shown on Fig. B-L In detail, the negative pulse of voltage of the lead H22 is impressed on the cathode and suppressor grid of the tube 32S, which is normally nonconducting because the control grid has a negative bias voltage. The tube 326 then conducts and so charges the condenser that the control grid of the tube 335 holds the tube nonconductive until. the charge leaks off through the resistors and 338, and the potentiometer The discharge time of the condenser is controllable by the potentiometer During the time the tube 33t is held in a nonconducting state, the anode voltage of the tube increases, thus forming a positive rectangular pulse of voltage, the duration of which is variable by the potentiometer 339. The crystal 3155 holds the maximum value of the voltage pulse at a constant predetermined value so that the output pulses are uniform. The voltage at the anode of the tube 335 is coupled to the control grid of the tube tl which is connected in the form of a cathode follower. A feedback circuit comprising the resistor 353 and the condenser 359 is connected between the cathode of the tube 341 and the control grid of the tube 3213K to improve the wave shape and response of the oneshot multivibrator circuit Ille'. The rectangular pulse of voltage taken from the cathode of the tube del by the lead 23 serves as the output for the invention and is shown on Fig. 3L.

Consider now, the operation of the invention as a unit rather than as individual circuits as described above. With the power supply Ill energized, the necessary operating voltages are sup plied to the individual circuits as shown on Fig. 1, and with the lead Ill connected to a frequency modulated system to be controlled, a frequency modulated signal voltage as shown on Fig. S-A is impressed on the limiter circuit 2t and the frequency selector circuit t. This frequency selector circuit 59 comprises the local oscillator and mixer tube 203 and the tuned anode circuit which can be tuned by the condenser 223 to pass a signal voltage at a predetermined frequency. The local oscillator frequency is adjustable by the coarse and fine tuning condensers 209 and 2 II to permit adjustment of the instantaneous frequency at which the heterodyne signal is obtained. Thus, for each excursion of the frequency modulated signal voltage, two output signal voltages are generated, one as the frequency is ascending and the other as the frequency is descending. These signal voltages are rectified by the crystal with the condensers- 209 and 2I I.

the-frequency of the local oscillator the first ofv the twoA output pulses of voltage can be made to occur early in the ascending frequency of the frequency modulated' signal voltage and the second pulse of voltage late inthe descending frequency. By raising the frequency of the local oscillator the frst of the two output pulses of voltage can be made to occur late in the ascending frequency of the frequency' modulated signall voltage and the second pulse of voltage early in the descending frequency'.

The frequency modulated signal voltage of the lead I'I I`v as shown on Fig. I-A is also impressed on the limiter circuit 20 which comprises the tube I5I and operates'` to remove` the amplitude modulation present on the signal voltage. and further serves as an isolation stage between the lead III and the following discriminator circuit 3U; The output'voltage of the limiter circuit 2E is coupled. from` the anode of thetube I5I` to the discriminator circuitl 30 by the lead IIZ` and is shown on. the Fig. 3-B.

Thus, the voltage of the lead II2 is impressed on the discriminator circuit 39, which comprises a transformerv H53 havinga tuned primary circuitl and havingV two tunedsecondary circuits, and a tube IBIy connected as a cathode follower. The primary tuned circuit is tuned to the mean frequency of the frequency spread of the modulated signal voltage. One of the secondary circuits of theftransformer. IGS is tuned toresonate at a frequency slightly above the resonant frequency of the primary winding,- while the other secondary circuit isftuned to resonate at a frequency slightly below that ofthe primary winding.` The crystals M59 and lfl rectify the alternating` output voltages of two secondary circuits so that a voltage is developed across the' resistors H2, tls, and Il which is proportional to the frequency of the modulatedsignalvoltage. These resistors are so connected to the two secondary circuits of the transformer |53 and to the control grid of the cathode follower tube IilI-l that the control grid is driven negative. at the highest frequency of the frequencyy modulated signal and positive at the lowest.freqiiency.y Since the voltage developed at the cathode of a cathode follower follows the voltage impressed at the controlv grid, the voltage off thelead: I Igwhich is connected to the cathode ofl the tube I8I, is substantiallyI a sine wave havingits minimum value coincident with the point of highest frequency of the frequency modulated signalv The voltagey of the lead IIs is shown on Fig: S-C and is coupled to the diferentiator and amplifier circuit Sill With the voltage of the lead H3 impressed on the control'grid of the tube 232, which is connected in the form of a conventional amplifier, the voltage isamplified and inverted at the anode of the tube as shown on Fig. 3-D. Since the combination of the condenser 242 and resistors 2li-B, 243, and 2&1!y is a differentiator circuit through which a voltage impressed is shifted in phase` by degrees,` the voltage of the control grid of the tube 24| is similar to the voltage of the anode of the tube 232 exceptfor the 90 degree phase shift and is shown as Fig. B-E'. The tube 24| is connected as a-cathode follower and couples the voltage output of the differentiator circuit to the control grid of the anode loaded amplifier tube 249. The positive portion of the voltage impressed on the control grid of the tube 249 overdrives the tube and the most positive portion of the voltage is thereby lost. Thus the anode voltage of the tube 249 has the wave shape as shown on Fig. 3-F. This voltage is coupled to the control grid of the tube 263 through the cathode follower tube 256. The tube 263 is overdriven during the `positive half-cycle of the voltage impressed on its control grid thereby completing the transformation of the sinusoidal input voltage to a rectangular output voltage at the anode of the tube 263. Thus, the voltage of the lead IM which is connected to the anode of the tube 263 is as shown on Fig. 3 G.

The voltage of the lead IM is connected to the gate circuit 8f3 and to the pulse generator circuit 40. The latter circuit comprises a gas discharge tube |89 which is connected tooscillate at a rate predetermined by the values of the resistor 29| and the condenser |93. The output voltage of the pulse generator 49 is synchronized by the voltage of the lead I I9 which is impressed on the control grid of the tube I 99 through a differentiator circuit comprising the condenser |9I and the resistors |92 and |93. The positive pulses of voltage developed by the differentiator circuit at the control grid of the tube |89 force the conduction of the tube when a pulse of voltage occurs at a time shortly before the condenser |98 has reached full charge, thereby synchronizing the oscillator with the voltage output of the differentiator and amplifier circuit 69. The output voltage of the pulse generator circuit 4U is coupled to the pulse type selector circuit 19 by the lead H9. i i

The pulse type selector circuit 19 comprises a manual switching arrangement and an electronic switch for selecting the manner in which the output voltage of the control circuit is developed. The manual switching arrangement shown in Fig. 7 comprises two ganged five-position selector switches 292 and 293. In the particular em bodiinent of the invention shown, only three of', the five available positions are utilized and will. be discussed; however, it is to be noted that the remaining two positions could be utilized for methods of pulsing other than those disclosed. With the ganged switches 292 and 293 in posi tion No. l, the output voltage of the `circuit `is aero. With the cranged switches 292 and 293 inl position No. 2, the output voltage of the circuit at the lead I 23 is controlled in such a manner that a rectangular pulse of voltage is generated at the desired frequency during the descendingi frequency of the frequency modulated signal. A further discussion of the positions Nos. 1 and 2 of the switches 292 and 293 will be given along with the discussion of the gate circuit 89 hereinafter. With the switches 292 and 293 in position No. 3, the electronic switch comprising the two tubes 213 and 219`becomes operative to influence the output voltage of the lead I 23. The lead I|1 normally has a positive voltage during the time the switches 292 and 293 are in position No. 3; however, when a positive sawtooth pulse of voltage is impressed on the differentiator circuit comprising the condenser 294 and the resistor 294, the control grid of the tube 219 receives a 14 negative pulse of voltage which` causes the `tube 219 to become nonconducting and the tube 213 to become conducting, thereby placing a negative voltageon the lead I|1. A short timelater a negative pulse of voltage is transmitted to the control grid of the tube 213 causing the tube 213 to become nonconducting and the tube 219 to I'I1. This control is `maintained by controlling the operation of the tube 3| I with the voltages of the lead II1. From the connections, previously described, it is seen that during thetime the control grid of the tube 3II is positive and the tube is conducting, there can be no output voltage at the lead I|9 `as the tube effectively removes positive pulses of voltage at its anode. the control grid of the tube 3I| is maintained negative by the voltage of the lead II1 the tube 3H is held in a nonconducting state and signal i voltages appearing at the anode of the tube are then coupled to the trigger circuit 99 by the lead H9. The lead ||4 furnishes a voltage as shown on Fig. 3-G to the control grid of the tube 39| and further controls the output voltage of the lead I I9 by alternately making the tube 30| conducting and nonconducting. During the time the tube 30| is conducting, the voltages impressed at the control `grid of the tube 391 have substantially no effect on thevoltage of `the lead IIS which is at a minimum value. However, when.

the tube 39| is nonconducting because of the negative voltage applied to its control grid by the` lead IM, the negative pulse of voltageof the lead |I8 causes the tube 391 tobecome nonconducting, thereby raising the anode voltage and developing a positive pulse of voltage at the lead I9. From the foregoing, it is seen: that a setting of the switches 292 and`293 of the pulse type selector circuit 10 inposition No. lmaintains the tube 3I| conducting and therefore holds the voltage of the lead I I9 at a minimum value, that a setting of the switches 292 and 293 in position No. 2 maintains the tube 3| I in a nonconducting state and therefore allows a positive pulse of voltage to be developed at the lead I I9 during the descending frequency of the frequency modulated signal as shown on Fig. 3-J, and that a setting of the switches 292 and 293 in position No. 3 causes the tube 3H to become nonconducting each time the pulse generator 49 develops a pulse of voltage at the lead IIS and therefore `allows a pulse of voltage to be developed at the lead ||9 at the predetermined rate of the pulse generH ato;` 4D. i, i

The positive pulses of voltage of the lead I I9 are then impressed at the control grid of the tube 3I3 of the trigger `circuit 9.9 `whichin` turn gencrates a negative pulse` of voltage at the leads |2| and |22 in response to eachpositive pulse of voltage of the lead II 9. The negative pulse of voltage of the lead |2I is impressed at the control grid ofthe tube 213 `of the pulse type selector circuit 'I9 to operate the electronic switch therein and return the switch to itsnormal operating condi-` When asi-acre tionaft'er each positive: pulse of voltage. of the lead I I6.

The one'z-sh'ot multivibrator' circuit It!) is controlle'd by the voltage of the lead 122 which is impressed at the cathode of the normally nonconducting. tube 3261 The tube 326 then conducts and the condenser 334 becomes charged in such a manner that the tube 336 is maintained nonconducting. untilv the charge of the condenser leaks off through the resistors 333 and 338 and theV potentiometer 339. By varying the effective resistance ofthe discharge path-of the condenser 3341 by changing the settingr of the potentiometer 339, it'ispossible'fto change the time during which the tube 336 is maintained in a nonconducting state. The positive rectangular voltages developed. at the anode of the' tube 336l are then coupled toy the' control gri-d ofthe cathode follower tube 34%?, and the rectangular pulses of voltage developedI at the cathode are then available to operate an external circuit by connecting the leadI |23E thereto;

TheA particular embodiment of the invention described was developed for use with a frequency mod-ulated cyclotron which: it was desired to operate with a pulsed arc. This invention accomplished the desired result by supplying a variable rectangular pulse of voltage to the arc electrodes of the cyclotron at any selected frequency within the descending frequency interval of the frequency modulated voltage applied to the accelerating electrodes. Several different methods of pulsing are provided by the pulse type selector circuit 'l0 and several other methods could be provided by a few si-mple additional connections.

While the salient features of this invention have been described in detailr with respect to one embodiment, it will, of course, be apparent that numerous modifications may be made Within the spirit and scope of this invention, and it is therefore not desired to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

l. In a control circuit for a frequency modulated system,the combination comprising means developing a voltage proportional to the frequency of the voltage ofa frequency modulated system, means shifting the phase of said proportional voltage and shaping said-k shifted voltage intoa-rectangular voltage, means developing a pulse of voltage at a selected frequency within the range ofthe frequency of the voltage of said frequency modulated system, a` gate circuit responsive to said rectangular voltage and said pulse of voltage and developing a pulse of voltage, andmeans responsive to the output pulse of voltage of said gate circuit` generati-nga rectangular pulse of voltage once during the excursion of the frequency of the voltage of said frequency modulated system at said selected frequency.

2. In a control circuit for a frequency modulatedv system, the combination comprising means developing a voltage proportional to the frequency of the voltage of a frequency modulated system, means shifting the phase of said proportional voltage and shaping said shifted voltage into a' rectangular voltage, means developing a pulse of voltage at a selected frequency within the range of the' frequency of the voltage of said frequency modulated system, means generating a-pulse of voltage at a predetermined frequency, a' gate-'circuit responsive tosaid rectangular voltage', said pulse of voltage obtained at said selected frequency, and said-y 4generated pulses of l'6 voltage, and means responsive to theout'put voltage of said gate circuit generating rectangular pulses of voltage with said predetermined frequency at said selected frequency.

3. In a control circuit for a frequency modulated system, the combination comprising means developing a voltage proportional to the frequency of? the voltage of a frequency modulated system, means shiftingthe phase of said proportional vol'tag'e' and sha-ping said shifted voltage .into a rectangular voltage, means developing a pulse of voltage at a selected frequency within the range' of said frequency modulated system, .meansl generating a pulse of' voltage at a predetermined.V frequency, a gate circuit responsive to said rectangular voltage and said pulse of voltage' occurring at said selected frequency, means controlling the operation of said gate circuit with said generated pulses of voltage, and means responsive to the output voltage of said gate circuit generating rectangular pulses of voltage at saidy selected frequency and having said predetermined frequency.

4. In a controly circuit for a frequency modulated system, the combination comprising a discriminator developing a voltage proportional to the frequency of the voltage of a frequency modulated system, a differentiator and amplifier shifting the phase of said proportional voltage and shaping said shifted voltage into a rectangular voltage, a frequency selector developing apulse of voltage at a selected' frequency within the range of the frequency of the voltage of said frequency modulated system, a gate circuit developing a pulse of voltage in response to said rectangular voltage and said pulse of voltage, a trigger circuit generating a uniform pulse of voltageA inV response to the pulse of voltage developed by said gate circuit, and a one-shot multivibrator responsive to said uniform pulse of voltage whereby a rectangular pulse of voltage of variable duration is produced once during the excursion of the frequency of the voltage of said frequency modulated system at said selected frequency.

5. In a control circuit for a frequency modulated system, t-he combination comprising a discriminator developing a voltage proportional to the frequencyof the voltage of a frequency modulatedV system, a differentiator and amplifier shifting the phase of said proportional voltage and shaping' said shifted voltage into a rectangular voltage, a frequency selector producing a pulse of voltage at a selected frequency within the range of the frequency of the voltage of said frequency modulated system, an oscillator generating pulses of voltage at a predetermined rate which are synchronize'd with said rectangular voltage, a gate circuit responsive to saidl rectangular voltage, to saidv pulse of voltage produced at said selected frequency, and to the pulses of voltage generated by said oscillator producing a pulse of voltage, a trigger circuit developing a uniform pulse of voltage in' response to the pulse of voltage produced' by said gate circuit, and a one-shot multivibrator responsive to said uniform pulse of voltage whereby a rectangular pulse of voltage of variable duration occurs at said predetermined rate of said oscillator and coincident with said selected' frequency.

6.The combination of claim 5 wherein the gate circuit comprises three triode vacuum tubes connected in parallel across a source of operating voltage, the control grid of the rst of said trodesbein'gnegatively biased beyond cut-off and connected to the output of said amplifier, the control grid of the second of said triodes being positively biased and connected to the output of said frequency selector, and the control grid of the third of said triodes being positively biased and connected to said oscillator whereby an output pulse of voltage occurs only when said three tubes are each in a cut-off state.

7. The combination of claim wherein the discriminator comprises a primary tuned circuit having resonance at the mean frequency of said frequency modulated system, a first secondary tuned circuit inductively coupled to said primary tuned circuit and having resonance above said mean frequency, a secondary tuned circuit induetively coupled to said primary tuned circuit and having resonance below said mean frequency, a rectifier connected to each of said secondary tuned circuits, and a resistance voltage divider network interconnecting said rectii'lers and secondary tuned circuits whereby a voltage proportional to the frequency of said frequency modulated system is developed.

8. In a control circuit, the combination comprising a source of frequency modulated voltage, a discriminator connected to said source for developing a voltage proportional to the frequency' of said modulated voltage, a diierentiator connected to the output of said discriminator and having characteristics such that the phase of the voltage applied is shifted at the output, an amplifier connected to the output of said differentiator for shaping the shifted voltage into a rectangular voltage, a frequency selector circuit connected to said source for forming a pulse of Voltage at a selected frequency, an oscillator con nected to the output of said amplier for generating pulses of voltage at a predetermined rate in response to said rectangular voltage, a gate circuit having three input circuits, one of said inputs being connected to said oscillator, the second input being connected to said frequency selector, and the third input being connected to said amplifier, whereby said gate circuit passes a pulse of voltage once during the frequency excursion of said modulated source voltage at said selected frequency.

QUENTIN A. KERNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,243,234 Von Duhn May 27, 1941 2,368,953 Walsh Feb. 6, 1945 2,414,479 Miller Jan. 21, 1947 2,434,294 Ginzton Jan. 13, 1948 

